This invention relates to magnetic seals for rotating shafts, and in particular, magnetic seals that allow for axial shaft movement.
Magnetic seals have proven reliable for use on rotary shafts. Magnetic seals have a stationary ring, referred to herein as a stator, and a rotating ring, referred herein as a rotor. The stator is generally fixed to the shaft housing and does not rotate with the shaft. The rotor generally rotates with the shaft. The stator and rotor touch through contact faces, which provides the seal between the stator and rotor. Obviously, the contact faces are subject to frictional forces.
Various means are employed to maintain the seal between the contact faces. Magnetic means are one method utilized to keep the stator and rotor contact faces in contact through the attractive forces of permanent magnets. The magnets can be positioned on either the stator or rotor, with the magnets interacting with ferrous materials in the opposite component. The features of magnetic seals are shown in U.S. Pat. No. 5,078,411 to Adams, hereby incorporated by reference. As is shown in Adams, the magnets can be positioned on either the stator (FIG. 7) or rotor (FIG. 4).
An improved magnetic seal is shown in U.S. Pat. No. 5,730,447 to Dawson. This patent discloses a xe2x80x9cfloatingxe2x80x9d inner annulus on the stator, which helps keep the contact faces in contact in the presence of shaft tilt or shaft misalignment. However, prior art magnetic seals have failed to address the issue of maintaining the proper relationship between contact faces in the presence of axial shaft movement. For instance, in either Adams or Dawson, a two component stator/rotor design is utilized which, when axial shaft movement occurs, may result in seal loss as the stator and rotor become separated.
Another problem with two component magnetic seals is the potential for the contact faces to become damaged. To effect a seal, the contact faces are lapped flat to high tolerances, such as 0.00001-0.00005 inches. In assembly, it is possible for the installer to scratch, nick or otherwise damage the contact faces. This can readily occur as the installer has access to both faces.
A final problem with magnetic seals is that some components of the seals may be joined to the rotating shaft with elastomeric O-rings. Over time, these rings can be exposed to heat and other stresses, and the rings may adhere or become semi-bonded to the shaft, preventing problems during periods of axial shaft movement.
It is therefore an object of this invention to provide a magnetic rotary seal, which allows unlimited axial shaft movement in either direction without seal removal.
It is an object of this invention to provide a single unit stator/rotor magnetic seal.
It is an object of this invention to provide an single unit stator/rotor magnetic seal easily installable, without the need for sleeves, drive collars, or other devices to set the seal into the shaft housing.
It is an object of the invention to provide a magnet seal where the contact faces are protected during installation.
It is also an object of this invention to protect the contact faces for exposure to contaminants during the operation and stand by modes of the machines it is installed on.
It is another object of the invention to free struck rotor O rings during periods of axial shaft movement.
The invention herein is a stator and a rotor, magnetically and mechanically coupled. The mechanical couple is provided through an interlocking annular groove provided on one component and a flange face on the other component. The mechanical couple allows the two components to become interconnected once a predetermined range of free movement of the rotor is exceeded. After the predetermined range is exceeded, the rotor slips along the shaft while the stator remains fixed.